Method for converting carbon monoxide into formic acid



Feb. 9, 1937. c. AMMON 2,070,503

METHOD FOR CONVERTING CARBON MONOXIDE INTO FORMIC ACID Filed June 7, 1934 Patented Feb. 9, 1937 PATENT OFFICE METHOD FOR CONVERTING CARBON MON- OXIDE INTO FORMIC ACID Christian Ammon, Berlin-Wilmersdorf, Germany Application'June v, 1934', Serial No. 729,538

In Germany 7 10 Claims. It isknown to make alkyl formates by interaction under pressure of carbon monoxide and water-free alcohols such as, for example, methyl alcohol, ethyl alcohol or propyl alcohol, in certain cases in the presence of metal alcoholate. It has also already been proposed to' convert the alkyl formates prepared in this way into formamide and ammonium formate with the aid of ammonia. From these compounds formic acid and ammonium sulphate may be obtained by interaction with sulphuric acid. Generally speaking, however, the technical production of formic acid is carried out almost exclusively by forming formates from carbon monoxide and alkali or alkaline earth hydroxides. The formic acid is then liberated in a second stage from the metal fo-rmates obtained thus by treatment with a mineral acid, e. g. sulphuric acid and is removed by distillation. Proposals have already been made directly to convert carbon monoxide into formic acid by attachment of water. However, the difficulties which beset a satisfactory solution of the problem on these lines are extraordinarily great (of U. S. Patents Nos. 1,606,394 and 1,895,238 among others).

The present invention relates to a process for converting carbon monoxide into formic acid, in which, in contradistinction to the processes usual at the present time, there is no consumption of alkali or alkaline earth hydroxide and mineral acid. As auxiliary substance for carrying out the process an alcohol is used, such as an 'alkyl alcohol (e. g. methyl alcohol, ethyl alcohol) which is continuously regenerated in the course of the process and led in circulation. The invention depends upon preparing alkyl formates in the manner known per se by the action of carbon monoxide on alcohols under elevated pressure, a reaction which is preferably carried out with use of metal alcoholates as reaction intermediates. The resulting alkyl formates, preferably separated from any free alcohol, are then hydrolyzed by water, which may have added thereto an acid as catalyst, into the constituents of the ester, viz. alcohol and formic acid. The former is freed from any ester and then interacted with carbon monoxide and converted into' alkyl formate, which is used again in the process, so that as regards the alcohol the process is cyclic.

It is advantageous to carry out the hydrolysis of the alkyl formate in several stages, preferably in so-called column apparatus (such as is used for separating mixtures of liquids), in countercurrent to the saponifying agent, viz. water or dilute acids. The hydrolysis must, of course,

June 17, 1933 be conducted at a temperature which does not exceed the decomposition temperature of the free acid. Since the individual reaction components are in mutual equilibrium it is also advantageous to promote the course of the hydrolysis by disturbing the equilibrium. This is advantageously effected by removing the alcohol formed by the hydrolysis of the ester with the portions of non-converted ester from the reaction space after one or several stages and supplying fresh ester each time to the following stage of the column. The rateof reaction may also be increased by carrying out the ester hydrolysis under pressure. The alcohol-ester mixture is separated in a separate column and resupplied to the circuit.

The present process has, as compared with the known processes for making formic acid, the advantage that no alkali or alkaline earth hydroxide and sulphuric acid are consumed and that a chemically pure product of any desired concentration can be obtained in continuous operation by suitably choosing the structural material for the plant used for the hydrolysis of the ester.

The process is described below in greater detail with reference to the accompanying drawing, both figures of which show columns suitable for carrying out the process described.

In Fig. 1 alkyl formates are supplied through .the pipe I at the bottom of the column. Water or diluted acid is supplied at the top at 2 and it flows through the various bottoms of the column in countercurrent to the vapours of the formic acid ester. The alcohol formed by the hydrolysis is withdrawn, with the portions of unsaponified ester, through the pipes 3, of which there may be any desired number, and is further treated in a separate separating column. Fresh ester, and if necessary, steam as Well, is supplied each time through the pipes d. The formic acid produced is withdrawn at 5.

In Figure 2 the formic acid ester is supplied through the pipe I. The vapours of the ester traverse the column in counter current to the water supplied at 2. The acid formed is withdrawn at 3 whilst the alcohol vapours with the portions of unsaponified ester are led through the pipe 4 to the second part of the column. Here the hydrolysis of the ester with suspensions of aluminium, chromium or iron hydroxide in water, which are supplied at 5, is carried to completion. The alcohol vapours leave the column through the pipe 6, and the product of the second interaction, a solution of aluminium, chromium or iron formate is withdrawn above the separating bottom at 1.

Example 1 Ethyl formate, obtained by the action of carbon monoxide on alcohol under pressure in presence of alkali or alkaline earth alcoholate, is separated from alcohol and alcoholate by rectification. 1500 kilograms of this ester are supplied to the column shown in Figure 1 through the pipe I. The addition of water, which is preheated to about C., is eifected at 2. Steam is supplied through the pipes 4 so that a temperature between 80 and 100 C. is maintained throughout the column. The quantity of steam and water supplied altogether to the system amounts to 500 kilograms. The formic acid produced is withdrawn at 5; a quantity of 1000 kilograms is obtained having a strength of The alcohol, together with the portions of unsaponified ester, escapes in the form of vapour through the pipe 3. This mixture is separated in the known manner into alcohol and ester in a separate column. The alcohol, after being dried, is returned into the ester-producing circuit, whilst the ester is subjected anew to the hydrolysis.

Example 2 1200 kilograms of methyl formate which have been obtained in an analogous manner to the ethyl formate of Example 1 are supplied through the pipe I under a pressure of 5 atmospheres to the V saponifying column shown in Figure 2. 400 kilograms of water which have been heated to about 120 C. are supplied at 2.

' Through the pipe 3 about 750 kilograms of acid are withdrawn. The vapours of methyl alcohol, unsaponified ester and water are Withdrawn at the head of the column and separated from one another by stepwise condensation.

The ester is then supplied anew in the form of vapour at the foot of the column. The water arising from the alcohol-water mixture is supplied again to the head of the column. After drying, the alcohol is converted again into methyl formate, by bringing carbon monoxide into r action with the methanol in known manner.

What I claim is:-

1. A method of making formic acid consisting in interacting carbon monoxide with an alcohol under superatmospheric pressure to form an alkyl formate, hydrolyzing the said alkyl formate to formic acid and alcohol, and separating the alcohol and interacting it anew with carbon monoxide for the purpose of making an alkyl formate for the process.

2. A method of making formic acid consisting in interacting carbon monoxide with an alcohol under superatmospheric pressure in the presence of metal alcoholate to form an alkyl formate, hydrolyzing the said alkyl formate to formic acid and alcohol, and separating the alcohol and interacting it anew with carbon monoxide for the purpose of making an alkyl formate for the process.

3. A method of making formic acid consisting in interacting carbon monoxide with an alcohol under superatmospheric pressure to form an alkyl formate, hydrolyzing the said alkyl formate under pressure to formic acid and alcohol, and separating the alcohol and interacting it anew with carbon monoxide for the purpose of making an alkyl formate for the process.

4. A method of making formic acid consisting in interacting carbon monoxide with an alcohol under superatmospheric pressure to form an alkyl formate, hydrolyzing the said alkyl formate to formic acid and alcohol at temperatures below the decomposition temperature of the free acid, and separating the alcohol and interacting it anew with carbon monoxide for the purpose of making an alkyl formate for the process.

5. A method of making formic acid consisting in interacting carbon monoxide with an alcohol under superatmospheric pressure to form an alkyl formate, hydrolyzing the said alkyl formate to formic acid and alcohol by treating the ester in countercurrent flow with a hydrolyzing agent, and separating the alcohol and interacting it anew with carbon monoxide for the purpose of making an alkyl formate for the process.

6. A process as claimed in claim 5 in which the hydrolizing agent is supplied to the ester stream at a pluralityof points in the line of flow of the latter.

'7. A process as claimed in claim 1 in which the hydrolyzing agent is water.

8. A process as claimed in claim 1 in which the hydrolyzing agent is dilute acid.

9. A process as claimed in claim 5 in which the hydrolyzing agent is water.

10. A process as claimed in claim 5 in which the hydrolyzing agent is dilute acid.

CHRISTIAN AMMON. 

